U.S. Pat. No. 4,429,990granted to E. J. Tamary Feb. 7, 1984 discloses a wicking structure for applying release liquid to the surface of a roller in a roller fixing apparatus. Release liquid, commonly referred to as "oil", is transported under pressure from a container to a permanent internal feed tube located inside a replaceable porous applicating wick. The feed tube and wick constitute a wicking or application roller which, when in contact with the fixing roller, is rotated by it while it "oils" the surface. This structure has many advantages including ease in articulation, efficient and rapid application of oil in response to an appropriate signal and quite low wear on the fixing roller surface.
The structure shown in the Tamary patent is commonly called a "rotating wick" and has been adopted commercially in a number of copiers and printers. The release liquid is delivered to the wicking structure using a pump through a feed means to a permanent, rotatable feed tube. The feed tube is cylindrical and has small distribution holes drilled or punched along its cylindrical wall through which liquid can pass. A replaceable wick surrounds the feed tube. It is installed by being pulled over the free end of the feed tube. The replaceable wick is a porous structure which includes an inner ceramic porous material that is covered by a porous and heat resistant fabric such as wool or a comparable synthetic fabric. The most commonly used such fabric is marketed by Dupont under the trademark NOMEX and is a well-known capillary fabric which is resistant to heat.
The ceramic core creates an air gap between the feed tube and any capillary material including the ceramic core. With that air gap, there is no danger of contact between the wicking material and the holes in the feed tube. If the wicking material contacts the distribution holes, any oil that is left in the tube when the pressure is removed is subject to wicking by the capillary material to greatly oversaturate that portion of the wicking material. This would ultimately create localized areas of heavy wicking on the roller with disasterous results to an image being fixed. Thus, the ceramic material helps spread the oil evenly around and along the wick, provides structural strength to the replaceable portion of the wick and separates the wicking material from the distribution apertures in the tube.
Although these wicking structures have been successful commercially, maintenance is complicated by the cost associated with the replaceable portion of the wick and by occasional clogging of the holes in the feed tube which clogging is not necessarily cleared merely by replacing the wicking structure. By far the most expensive item in the replaceable portion of the wick is the ceramic core.
U.S. Pat. No. 4,908,670 granted Mar. 13, 1990 to S. L. Ndebi suggests a wick for a fusing roller which includes a disposable feed tube in which care is paid to the size and/or shape of apertures through which the liquid passes and a soft porous capillary material surrounding the tube itself. This structure improves the reliability of the overall rotating wick device because the tube itself is replaced with the rest of the wick. It also sunstantially reduces the cost of the wick by eliminating the ceramic core.
Although this structure has these advantages of increased reliability and reduced cost, it works best with high viscosity oil.